Neon display signs while very bright are expensive to produce and subject to high operating and maintenance costs. The maintenance costs may be as high as 30% or more annually and include glass tube breakage, transformer failure, corrosion, electrical shorts that cause fires, hazardous disposal requirements and other costs. Neon signs in addition operate at from about 3,800 to 15,000 volts. Other kinds of lamps such as high intensity discharge, HID, metal halide lamps are rarely used because replacement lamp cost, short lamp life, high heat inside sign box cavities and hazardous disposal of failed lamps. Florescent lamps have shortcomings similar to HID lamps with the exception of lamp cost. Consequently, light emitting diode (LED) lighting is preferred for use in the present invention.
Backlit LED display signs that are in commercial use, exemplified by U.S. Pat. No. 6,717,526, often employ 100 or more LED lights which are generally positioned about ½ inch to 1 inch apart in rows, columns, and lines usually aligned beneath a symbol, a word, or letter to be illuminated on a front cover of the sign. This construction makes the sign expensive and complicated to construct. In some prior LED signs, the LED's or other lights are spread somewhat farther apart but at a substantial reduction in brightness which makes the sign less useful especially for daytime operation and gives the sign less marketing appeal because it appears dim compared, for example, with a neon sign of comparable size. Moreover, the brightness of some signs varies from one part of the sign to another, a condition sometimes referred to as “hot spots”, which is, of course, unacceptable. Other attempts to produce signs with LED's spaced more than an inch or so apart have only resulted in signs that exhibit “hot spots”, and have a depth of over 5 inches which makes them unsuitable for many applications. By contrast, an important objective of the present invention is to provide a sign that is no more than 3 inches in depth, yet is free of “hot spots”.
U.S. Pat. No. 6,236,382, for example, describes an LED display unit having a lens to which a light diffusion material has been added. However there is no provision for channeling, confining, or guiding light rays within a sign element or for producing visible symbols on the front surface of the lens. U.S. Pat. No. 6,717,526 describes an LED lighting device with rows of lights, each made up a great many LED's, e.g. 27 LED's in a single row that can be used, for example, as a traffic signal. In this case, rows of LED's are covered by a multiple collimating element made of acrylic that has multiple circular or linear collimating zones arranged to match the concentric circles or linear rows of LED's but there is no provision for confining or guiding light within a sign element or for producing an image representing letters or numbers on the front surface of the device.
U.S. Pat. No. 6,978,566 describes a backlit sign that employs LED's enclosed beneath a transparent colored layer and a transparent plastic sheet that has printed symbols on the rear or inside surface of the plastic sheet. Again, there is nothing within or upon either the plastic sheet or the translucent colored layer to confine, direct or channel light rays through a body of light-transmissive material prior to being emitted to enhance the image on the front surface of the sign. Moreover, black undercoating layers that are used absorb incident light present within the milky-white cover thereby reducing the brightness of the sign. U.S. Pat. Nos. 6,598,328 and 6,641,880 disclose plastic films that can be used in a sign but do not disclose the construction of a complete sign nor a low LED density sign construction.
In view of these and other shortcomings of the prior art, it is one object of the present invention to provide a backlit display sign employing one or more point light sources such as an LED light source to illuminate at least one opening at the front of the sign to produce a line, symbol, alphanumeric representation, or other indicia including a provision for efficiently channeling light energy to the opening on the front of the sign to achieve a level of brightness comparable to that produced by a neon sign of a similar size but at a much lower operating cost and with far fewer LED's than are currently required.
Another object of the invention is to provide a backlit display sign of the type described which has features that make it possible to use a small number per area, e.g. 1 LED per ft.2 in a sign with an efficiency high enough so that the LED's no longer need to be placed in rows, columns, or lines aligned under openings where the light is to be visible on the front surface of the sign and yet does not exhibit “hot spots”.
Another more specific object of the invention is to provide an improved backlit display sign characterized by brightness similar to that of a neon sign even though illuminated by LED's at a low density per unit area of sign coverage, by which is meant that the LED's are more than 2 inches apart.
Yet another object of the invention is to provide a backlit display sign which is rugged in construction and more quickly and readily manufactured at a lower cost than prior signs yet provides outstanding visibility, light uniformity and sufficient brightness to make it suitable for daytime use.
Another object of the invention is to provide a sign of the type described which is virtually free of bright spots or other objectionable variations in the amount of light emitted throughout the sign while at the same time making it possible for the sign to have a shallow depth from front to back.
A further object of the invention is to provide a backlighted display sign with a feature for more efficiently collecting, directing, guiding, and emitting light in specific areas where symbols, letters, and numbers are to appear so that a sign of commercially acceptable brightness can be achieved with a small number, typically a total of 1-5 LED's.
Still another object is to provide a display sign of the type described which exhibits outstanding brightness yet has a depth of only about 3 inches or less.
Another object is to provide an LED light display that consumes about 30-80% less electrical power than similar commercially available LED light displays of similar brightness.
These and other more detailed and specific objects of the present invention will be better understood by reference to the following Figures and detailed description which illustrate by way of example but a few of the various forms of the invention within the scope of the appended claims.